Stand by for the most hotly contested UK advertising pitch of the year – the £110m (Nielsen) Tesco account is up for grabs.

But don’t hold your breath for a result. This is going to be a long-drawn-out contest, meticulously referee’d at every stage by agency intermediary Oystercatchers. Not a cosy inside job, pushed through on a nod and a wink from Tesco’s C Suite, as has tended to be the case in the past.

The first stage, happening quite soon, will be the selection of 13 agencies for a credentials presentation. From these, 6 will be invited to pitch, 3 will be eliminated and the winner will emerge in, oh, July some time. If all goes according to plan. So, expect the air to be thick with speculation over the next 4 months.

Let’s be clear before going any further. What’s particularly interesting about this pitch is not the fact that it is taking place now. Few readers will have failed to notice a changing of the guard at Britain’s top retailer, starting with the departure of group chief executive Sir Terry Leahy about a year ago and his replacement by Phil Clarke. Clarke is clearly a man who knows what he wants, and has wasted little time letting his senior colleagues know it too. Out went one-time rival for the top job Richard Brasher, until very recently UK CEO, after some lacklustre performance in the core operation and in came (a little earlier, as it happened) David Wood, late of Tesco Hungary, as head of UK marketing to replace Carolyn Bradley; meantime micro-managing Clarke has seized the UK helm himself.

Equally evidently, Clarke has been under heavy pressure from shareholders to shake things up, pronto. Tesco is still the UK’s biggest grocer by a wide margin, but it is a declining one. Others – practically all its leading rivals in fact – are bettering it in today’s tough market. Earlier this year, Tesco had to do the unthinkable: issue its first profit warning in 20 years, which knocked about £4.5bn off its stock market valuation in one day.

Personal animosity certainly came into Brasher’s dismissal, but there is little doubt that he was a convenient scapegoat too. And maybe with good reason. Brasher’s Big Price Drop campaign was a prelude to a disastrous Tesco Christmas. Brasher also held some rather fixed views on long-term investment. Whereas, what shareholders actually want is profits now, not in some misty future. Clarke knows that a second profit warning will effectively be his corporate suicide note.

So no pressure, Phil, to review your strategy. Ordinarily, UK advertising might seem to bat fairly low in a retail group CEO’s priorities – way beneath, for example, such operational issues as how many and what sort of new stores to open. Not so here, however. In giving Brasher the heave-ho and replacing the muddled duarchy at the top of UK management with a more focused leadership – himself – Clarke is also implicitly challenging Tesco’s long-established marketing tradition. Note that Brasher – like Leahy – came up the marketing route; before being promoted to UK CEO in March 2011, he had been UK marketing supremo since 2006. Clarke, on the other hand, is grounded in operations and IT, not marketing.

That’s why the key word associated with this advertising review is “clarity”. Having brought more focus to UK leadership, Clarke also intends to bring more focus to Tesco’s UK marketing effort. And he’s going to do it by asking some fundamental questions about Tesco’s current positioning. Are the assumptions underlying ‘Every Little Helps’ still relevant in today’s market? How does Tesco’s current marketing strategy benchmark against that of its apparently more successful UK rivals? Has the Tesco brand become too arrogant and impersonal – through servicing the requirements of the City rather than its customers? Clarke wants ideas from his agency pitch list, not just a new colour chart.

Superficially, this looks like bad news for the incumbent agency of 6 years, The Red Brick Road (or Ruby, or whatever the new digitally-enhanced business is going to be called). Although asked to repitch, it is indissolubly linked to the very marketing tradition that Clarke seems hell-bent on changing. Lineally, TRBR is descended from Lowe Howard-Spink; and the strong historic relationship forged between Lowe founder Sir Frank Lowe and Tesco top brass Leahy and his chief marketer Tim Mason. When Sir Frank split from Lowe & Partners (as it was by then called), Tesco backed his breakaway TRBR, but only on condition that Lowe creative chief Paul Weinberger was an integral part of the deal. To this day Weinberger, now chairman of TRBR, is the key mediating figure on the Tesco account (Lowe himself having retired).

That said, there are plenty of good reasons why Tesco might choose to retain TRBR’s services.

First, alone among competing agencies, TRBR will be the one tailored specifically to Tesco’s requirements. (Indeed, many would say this is its primary problem as a diversified advertising agency: despite doing good work for the likes of Magners cider and Thinkbox, it has failed to shake off the image of being Tesco’s house agency.)

Second, notice that Tesco has been careful not to pull the rug entirely from under TRBR. Up for grabs is all the consumer-facing digital and traditional (ie television, press, radio and outdoor) advertising. But not, you’ll observe, trade advertising, which is a substantial part of the overall TRBR fee package. One explanation for this, no doubt, is the sheer complexity of trade marketing; but Tesco also seems to be sending a mildly positive signal to its agency of longstanding.

Third, since this review is really about positioning rather than a creative makeover or a new catchline, don’t underestimate the skills of David Hackworthy and his TRBR planning department.

Fourth, don’t forget that Tim Mason is part of the review team. It’s surely only a matter of time before shareholders get their way and have Clarke cauterise the eye-watering losses at US venture Fresh & Easy, on which Mason currently spends two-thirds of his executive time. That will free more time for Mason’s other two roles as group deputy chief executive and, more pertinently here, group CMO. (It’s also possible that he might choose at that point to bow out; but no one should bank on it.)

Who else will compete for the account? Many prime candidates with suitable retail experience – BBH, DLKW/Lowe, Fallon, AMV BBDO, Rainey Kelly Campbell Rolfe/Y&R – are excluded precisely because they have conflicting supermarket accounts. However, Tesco has made it clear it will look tolerantly upon other kinds of agency conflict: for instance, a clash in financial services or telecoms.

That leaves plenty of possible contenders. As my associate Stephen Foster at MAA has pointed out, Publicis London is surely one of them. Historically, it was keeper of the Asda account and is now captained by former TRBR managing director and Tesco account director Karen Buchanan.

But the hot money will be on WPP. There’s some unsettled business here. Those with keen memories for this sort of thing will recall that, 7 years ago, WPP agency JWT came close to winning a big supermarket account after hiring two key Tesco agency players, Mark Cadman and Russell Lidstone, from a clearly flagging Lowe.

From what I hear, WPP is putting every resource possible behind winning the Tesco trophy. Not only is JWT throwing its hat into the ring; so are Grey, Ogilvy, 24/7 Media and CHI. Though whether individually or as part of a WPP “Team” effort I don’t yet know.

However, WPP agencies should tread with care.

Tesco will surely be aware, or have been made aware, that there is a certain amount of bad blood between Britain’s best-known agency intermediary Oystercatchers (founded by Suki Thompson and ex-JWT new biz director Peter Cowie) and Britain’s best-known and biggest marketing services company, WPP. Namely, the Everystone breakaway affair and its litigious sequel, which came to an unhappy conclusion about a year ago.

The formality of Tesco’s pitch procedure and its choice of intermediary suggests that there is no easy inside-track here for WPP chief Sir Martin Sorrell. I suspect his best course will be to keep an uncharacteristically low profile for the duration of this pitch.